This invention concerns an ejection device for a movable furniture part with a lever for transferring force to the movable furniture part. The lever has a lever body which is pivot-mounted within limits around a fulcrum point, and the lever body has a free end.
Ejection devices of this type have been used for a long time. A torque M is applied to the lever body by an actuator, usually an electrical device. If the ejection device is arranged in a furniture body, the force F exerted by the lever body on the movable furniture part with a moment arm r is given by the formula F=M/r.
Given a torque M exerted by the actuator, it follows that the force F applied to the movable furniture part is smaller, the longer the moment arm r. Of course, the magnitude of the moment arm r corresponds to the distance between the fulcrum point and the position where the lever body contacts the movable furniture part. Since, according to the state of the art, the lever body rests on the movable furniture part with its free end, the moment arm r usually corresponds to the length of the lever body.
Since the distance over which the lever body can apply a force F to the movable furniture part before the movable furniture part clears the lever body is affected by the length of the lever body, the lever body cannot be configured too short.
FIG. 1a shows in diagrammatic form an ejection device 1 with a housing 5 to which a lever 2 is pivot-mounted such that it will rotate within a limited angle. The ejection device 1 is assembled to a carrier element 6 and comprises an electric motor (electrical actuator) 15 to actuate the lever 2. The carrier element 6 is arranged on a furniture body 16 (see FIG. 10). Lever 2 comprises a lever body 3 having a base (fulcrum) end and a free end 4. An idler roller 7 is arranged on the free lever end 4. FIG. 1a deals with a drawer 17 (see FIG. 10) as the movable furniture part 8 which is resting in the closed end position in the furniture body 16. The idler roller 7 rests on a rear wall of the drawer.
FIG. 1b shows the force F exerted by the lever on the rear wall of the drawer and plotted versus path s. In this, the path s refers to the distance covered by the rear wall of the drawer from the closed end position to the point where it loses contact with lever 2. FIG. 1c shows a graph of the current drawn by the electric motor over the path s. The problem in this state of the art is that the force acting on the movable furniture part at the start of the ejection path s is relatively small.
As shown in FIG. 2a, an attempt was made, therefore, to improve the arrangement by adding a further roller 7 about half way along the lever. (This design is not a part of the invention).
It follows from FIG. 2b that this measure actually results in a considerable rise in the force F exerted initially on the movable furniture part 8. However, a significant disadvantage in this design version can be deduced from FIG. 2b and FIG. 2c, namely, that as soon as the lever 2 has swung out to the point where the second roller 7, arranged at the free lever end 4, comes to rest on the movable furniture part 8, a leap occurs in the force F and current I. This leap is based on the fact that when the second idler roller 7 comes into contact with movable furniture part 8, the effective moment arm r suddenly lengthens, causing a sudden reduction in the force F. As FIG. 2c shows, this leads to a sudden increase in the current I supplied to the electric motor, since the latter needs an increase in torque M to supply the same force F now that the moment arm r has lengthened. Since the only way that this can be done is at a lower motor speed, the motor is forced to slow down.
This exposes the disadvantage in the state of the art in that, due to the long moment arm r, only a small force F can be applied to the movable furniture part. In the initial acceleration phase in particular, in which the movable furniture part has to be accelerated from a rest position by overcoming its mass inertia, this causes a high load on the actuator and a slow ejection process due to the slow acceleration.